Add unused client cleanup configuration

[jjg-123]

As per https://oa4mp.org/server/manuals/unused-client-cleanup.html
Probably add the following to the configuration

<unusedClientCleanup gracePeriod="6 hr"
                     deleteVersions="false"
                     enabled="true"
                     interval="4 hr">
    <whitelist>
       <clientID>localhost:template</clientID>
    </whitelist>
</unusedClientCleanup>

which gives a grace period of 6 hours and checks every 4 hours and it skips the template.

[jjg-123]

Be sure to enable issue 14 first and let it run for a bit first to make sure there is data there.